1. Field of the Invention
The present invention relates to techniques for measuring shock pressure, and more specifically, it relates to fiber-based, optical pressure-sensing methods.
2. Description of Related Art
Shock waves are pressure waves with a very short rise time, and are produced in both impact and explosive phenomena. Dynamic experiments with shock waves require a tool to measure relatively large, rapid pressure changes.
A desirable shock pressure sensor would offer fast (sub-microsecond) response, a large dynamic range, and a non-perturbing interface that is easily adaptable to a variety of systems to be studied. In addition, because shock waves often involve high ultimate pressures that often destroy the sensor, the sensor element exposed to the shock must be inexpensive. Piezo-electric, piezo-resistive and electrical pin gauges are the most commonly used sensors for many shock experiments, but they all require electrical connections and wires which are awkward for some applications. In addition, fast movement of the wires as a result of the shock can cause spurious voltages that compromise the measurement. Finally, the wires themselves are an intrusive, complicating factor, as they can conduct heat out of the system, and can change the density and shock velocity profile of the system substantially, perturbing many types of coincident measurements of interest.
Optical methods are useful for measuring large, static pressures, with good sensitivity and large dynamic range. In the common scenario of measuring pressure inside a diamond anvil cell, a small, non-intrusive chip of ruby is placed inside the cell. An external light source, usually a low-power laser, is used to excite the ruby, and the observed fluorescence peak position indicates the pressure. Ruby fluorescence, however, takes place on the order of several microseconds, and becomes even slower as pressure increases, too slow to be useful for many shock measurement systems. Pressure-induced Raman shifts have been used in similar arrangements to indicate pressure, but Raman scattering is a weak effect, and the shift observed is fairly small. Thus, it requires either long measurement times, or extremely powerful and difficult to use laser light sources. Measurements of a microsecond or less strain the limits of technical possibility. Therefore, improved techniques for measuring shock pressure are greatly desired.